Method for production of a lens and lens produced thus

ABSTRACT

In a method for producing a lens ( 2 ), in particular a spectacle lens, central aberrations of an eye ( 1 ), to be corrected, of an ametropic person, such as sphere, cylinder and axis, are compensated. At least one refracting surface ( 9, 10 ) of the lens ( 2 ) is configured such that for at least one direction of view both a dioptric correction of the ametropia is performed and aberrations of higher order are corrected. Their effects on the visual acuity and/or the contrast viewing are a function of the size of the pupillary aperture ( 5 ) of the eye ( 1 ) to be corrected and are corrected by the lens ( 2 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for producing a lens, in particular aspectacle lens, central aberrations of an eye, to be corrected, of anametropic person, such as sphere, cylinder and axis, being compensated.The invention also relates to a lens that is produced using the method.

2. Description of the Related Art

Ametropias of eyes are generally corrected with the aid of spectaclelenses or contact lenses, in order to increase the visual acuity. Forthis purpose, the refracting values, such as sphere, cylinder and axis,of the spectacle lens or the contact lens that are optimum for raisingvisual acuity are determined in a subjective or objective measuringmethod. These data are then incorporated in a known way into a spectaclelens having two refracting surfaces, in which case the surface avertedfrom the eye is generally a spherical surface and, given the presence ofan astigmatism, the surface facing the eye is a toric surface rotated infront of the eye in accordance with the axial position.

Aberrations occurring in the case of a lateral view through a spectaclelens are reduced by using aspheric and atoric surfaces, aspheric andatoric surfaces constituting surfaces that deviate from a sphere or atorus, respectively. The use of such surfaces for reducing aberrationshas already been practiced for a long time. Likewise known areirregularly shaped surfaces, so-called freeform surfaces, which areused, in particular in the case of progressive lenses, to achieve therise in power in the near zone in order to support the accommodation.The production of such surfaces with the aid of CNC-controlled grinders,millers and polishing machines is likewise known from the prior art.

Furthermore, refractive measuring methods such as wavefront detection,are known that not only permit the values, already mentioned above, ofsphere, cylinder and axis to be determined, but also aberrations ofhigher order over and above this. These aberrations are a function ofthe aperture of the eye pupil.

The size of the pupillary aperture is influenced, inter alia, by thebrightness of the surroundings, medicaments, and the age and healthinessof the person being examined. In healthy adults, the pupillary aperturefluctuates between 2.0 mm and 7.0 mm. The pupillary aperture is smallerin daylight than in twilight or at night.

A refractive measuring method is known from EP 663 179 A1. The documentdescribes a method with the aid of which refractive measurements canalso be undertaken on an eye provided with a contact lens. Measurementsare undertaken at different points of the contact lens/eye system. In afirst step, a light beam is generated whose light source is selectedfrom a group that comprises a plurality of point light sources andslit-shaped light sources. Thereafter, this light beam is guideddirectly into the eye onto the retina, and the light beam is reflectedstarting from there. The reflected light beam therefore strikes ascanning aperture. The passage of light through the scanning aperture ispicked up by a camera, which generates an image signal. This signal isdisplayed on a monitor. The method and the device, as well, are ofsubstantial use for measuring optical defects, deformations oraberrations of an eye.

Furthermore, DE 199 54 523 discloses a production method for contactlenses, the first step being to use a so-called wavefront detectionmethod to determine the optical ametropia of an eye, and a soft contactlens being mounted on the cornea. The refractive measurement is carriedout with the contact lens seated, a material removal method supported bylaser radiation thereafter being applied on the contact lens separatedfrom the eye. Owing to the removal of material supported by the laser,the contact lens assumes a surface shape by means of which a surfacepower that is determined by the optical correction data is obtained inthe contact lens. Furthermore, information relating to the surfacetopology of the eye is obtained, and is likewise also incorporated intothe correction.

U.S. Pat. No. 6,224,211 discloses a method that, in addition to thecorrection of the normal atropia, also permits a correction to thespherical aberration of the eye. Various aspheric contact lens that aredesigned for zero spherical and astigmatic action are mounted on the eyein each case. These lenses are used to determine how the sphericalaberration of the eye can be corrected as best as possible. Thisinformation is used to determine an aspheric lens, which permits theoptimal correction of the visual acuity and is matched to the patient.

Finally, DE 100 24 080 A1 discloses a method with which the completecorrection of ametropias of the human eye is to be possible, a wavefrontanalysis device being used for this purpose. The substance of the aimhere is a surgical correction of the eye itself. The dependence of thepupillary aperture on the aberrations of higher order is not taken intoaccount.

The size of the pupillary aperture is 3.0 mm to 3.5 mm in daylight forhealthy middle aged adults. With increasing age it decreases toapproximately 2.0 mm to 2.5 mm. Since the size of the pupillary aperturecan enlarge up to 7.0 mm as darkness grows, the effects of errors ofhigher order change as a consequence.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to create an alternativemethod that permits a spectacle lens to be produced such that theoptical surfaces of a lens can be configured in such a way thataberrations of higher order are substantially reduced, and thereby aspectacle lens is produced that permits maximum visual acuity.

According to the invention, this object is achieved by configuring atleast one refracting surface of the lens such that for at least onedirection of view both a dioptric correction of the ametropia isperformed and aberrations of higher order whose effects on the visualacuity and/or contrast viewing are a function of the size of thepupillary aperture of the eye to be corrected, are corrected by thelens.

Aberrations of higher order that are a function of the pupillaryaperture are chiefly the spherical aberration, astigmatisms of higherorder the coma, and the trefoil (three leaf clover) aberration. Theseare deviations from the ideal paraxial image. It is understood asregards spherical aberration that incoming paraxial beams strike thelens at different heights of incidence, and so the paraxial beam cutsthe optical axis at the focal point F′, while the beams incident atfinite heights have other intercept distances.

Coma is generally understood as the aberration which occurs in the caseof the imaging of off-axis object points by beams with a large apertureangle, and in which spherical aberration and astigmatism aresuperimposed and which is proportional to the object—and the square ofthe pupil height to a third order approximation. What results in thiscase is an unsymmetrical aspheric comet-type scattering figure whosetail respectively points away from or to the optical axis in the case ofexternal or internal coma, and a corresponding point image spreadfunction having only partially formed diffraction rings. Trefoilaberration is understood as an aberration of higher order that generatesvia a wave aberration a three-way point image spread function with adefinition brightness. The trefoil aberration is superimposed on thecoma of 3rd order and remains as residual aberration if only the imagingof the meridional and sagittal rays are corrected. This gives rise tothree-way stars as image points.

Refractive measuring methods such as, for example, the wavefrontdetection method are used to determine the refraction values of theametropic eye, which means that the sphere, the cylinder, and the axisare determined. Moreover, cylinder, and the axis are determined.Moreover, this method can be used to carry out transmitted-lightmeasurements through the cornea, the eye lens and the vitreous humor andthereby the aberrations; of higher order that are a function of thepupillary aperture are determined. The result includes the aberrationsthat arise from the combination of the optical effects of cornea, eyelens, vitreous humor and pupillary aperture.

The information obtained can thus be incorporated into at least onerefracting surface, chiefly the rear surface of the spectacle lens, byusing the methods of calculation and production corresponding to theprior art.

A spectacle lens is thus designed that, in addition to the errorspreviously correctable, which are described by the paraxial values ofsphere, cylinder, axis, also compensates those which are a function ofthe aperture of the pupil. As a result, spectacle lenses that offer thespectacle wearer a substantially higher visual acuity for at least onedirection of view are created for ametropic and for emmetropic(correctly sighted) persons. The best possible visual acuity istherefore provided not only by a correction to the paraxial values, butalso by a correction to the aberrations of higher order.

It can be provided in an advantageous way that the region of the highestvisual acuity is formed by introducing at one aspherical surface.

The design of the region of most acute vision as an asphere is veryadvantageous by virtue of the fact that this refracting surface deviatesfrom a spherical surface. The surface deviates from a spherical surface.The lens curvature thus differs from a spherical surface, axially remotebeams being refracted more weakly or more strongly than in the case ofthe use of a spherical surface, and it thereby being possible to reunitethe light beams at a focal point F′.

Exemplary embodiments of the invention are explained in more detailbelow with the aid of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustration of the principle of a beam bundle in thecase of uncorrected spherical aberration;

FIG. 2 shows an illustration of the principle of a projected originalpattern;

FIGS. 3 a and 3 b show illustrations of the principle of a reflectedprofile with distortions;

FIG. 4 shows an illustration of the principle of a beam bundle in thecase of corrected spherical aberration;

FIG. 5 shows a depiction of the uncorrected spherical aberration of aneye;

FIG. 6 shows an exemplary depiction of an illustration of the correctionof the spherical aberration; and

FIG. 7 shows an illustration of a sagitta h, which is defined as thedistance between a vertex S of a spectacle lens and a. nadir point L onan optical axis.

DETAILED DESCRIPTION

FIG. 1 shows the system of an eye 1 in conjunction with a lens 2. Thelens 2 is preferably a spectacle lens, but it can, of course, also be acontact lens or an intraocular lens. The lens 2 can be formed from glassand/or plastic. It is also possible to provide for different lenses 2,for example contact lens and spectacle lens, to be combined with oneanother so as to correct the ametropias. The light beams 3 emanatingfrom an object (not illustrated here) transit the optical system ofspectacle lens 2 and reach through a cornea 4, an eye pupil 5 and an eyelens 6 to the retina 7 of the eye 1. Located on the retina 7 is a foveaof the eye 1 at which the greatest density of the photoreceptorsprevails. Ideally, all the optical information should be directed intothe fovea. This means that the fovea on the retina 7 constitutes a focalpoint F′ at which the light beams 3 should intersect at a point.However, this is achieved only for small pupillary apertures. Because ofthe spherical aberration occurring with every eye 1, not all the lightbeams 3 that transit the eye lens 6 are united at the focal point F′ orin the fovea on the retina 7. The beams 3 incident further toward theedge of the pupil 5 cut the retina 7 generally at points further removedfrom the ideal intersection point F′.

Since what is involved here is the correction of in principle any eye,that is to say also the correctly sighted (emmetropic) eye, the lens 2in the depiction of FIG. 1 is illustrated only as a drawing of theprinciple.

In order to remove the spherical aberration, it is firstly necessary toobtain specific information on the ametropic eye 1. Use is made for thispurpose of the wavefront detection method, which operates by using awavefront aberrometer, for example a Hartmann-Shack sensor.

A pattern of individual light beams that is illustrated in FIG. 2 isimaged onto the retina 7. A distorted image of the incoming light bundle3 owing to the aberrations of the eye 1 is produced on the retina 7. Anintegrated CCD camera, which is installed coaxially with the incidentbeam 3, picks up the distorted image at a very small solid angle atwhich the image is defined free from aberrations. An offline programcalculates the aberrations with the aid of a desired/actual comparisonof the relative positions of the incident partial beams 3 in relation tothe relative positions of the points produced on the retina 7.Thereafter, the aberrations are described mathematically by coefficientsof Zernike polynomials and are represented as a height profile. Theprofiles reflected in FIGS. 3 a and 3 b are provided with two differentdistortions of the original pattern. FIG. 3 a shows a less distortedprofile with reference to FIG. 3 b.

The system of an eye in conjunction with a lens 2 with correctedspherical aberration is illustrated in FIG. 4.

The measurement of the eye 1 with the aid of a wavefront detectionmethod yields an accurate conclusion about the imaging properties of theeye 1 and, in particular, about the aberrations which are a function ofthe pupillary aperture 5. In order to determine the imaging propertiesof the eye 1 or the paraxial values of sphere, cylinder, axis of the eye1, it is possible to use any designed unit that can supply thewavefronts specifically required here.

Of course, the paraxial values can also be determined via a refractivemeasurement or with the aid of skiaskopy. These values can be determinedby an optician or by an ophthalmologist, for example. Skiaskopy isunderstood as a manual method for objectively determining the refractionof the eye. In this case, the directions of movement of light phenomena(secondary light source) are observed on the retina of the subject's eyeand conclusions are derived therefrom regarding the ametropia.

Likewise, the size of the pupillary aperture 5 is determined by means ofthe wavefront detection method for the purpose of correcting theaberrations of higher order. Since the pupillary aperture 5 for daylightdeviates clearly from that for twilight, it follows that the visualacuity of a person can also change. It can therefore be expedient toadapt to such a person first lenses 2 for correcting the ametropia byday, and further lenses 2 for correcting the ametropia in twilight. Ifappropriate, it is also possible if required to adapt further lenses 2,for example for seeing in twilight, as a function of the pupillaryaperture 5 and the visual acuity determined in this case.

The information obtained is used via appropriate optical calculationsfor the purpose of modifying at least one surface of the lens 2, thisexemplary embodiment referring to a rear surface or an eye-side surface9 of the lens 2, in the surroundings of a viewing point 8 such that theideal union, already described above, of the light beams 3 is realizedat the fovea of the retina 7. The eye 1 is measured without the lens 2,a deformed wavefront being produced. In order to remove the sphericalaberration, a wavefront should be produced that is formed oppositely tothe already existing wavefront. The information of the oppositewavefront is introduced into the lens 2 on the rear surface 9 in thesurroundings of the viewing point 8 in such a way that at least oneaspheric surface is produced.

Here, aspheric surface is understood, in particular, as the section froma rotationally symmetrical surface that differs, however, from thespherical shape. Thus, as a result of the configuration of the asphere,the light beams 3 intersect at a focal point F′ of the fovea on theretina 7. The spherical aberration is thereby removed. Depending on thetargeted improvement of the visual acuity, the surface can likewise bean atoric surface or a freeform surface.

An atoric surface denotes a section from a surface that has two mutuallyperpendicular principal sections of different curvature, and in the caseof which the section through at least one of the main sections is notcircular.

A free form surface is to be understood as an asphere that is neitherrotationally symmetrical nor axially symmetrical.

The correction of the spherical aberration, also termed apertureaberration, of the eye 1 can likewise take place with the same action ona surface 10, averted from the eye 1, of the lens 2. Corrections canlikewise be realized on both surfaces 9 and 10 of the lens 2.

A correction of the spherical aberration is basically possible for allshapes of lenses, in particular all shapes of spectacle lenses. In thecase of single-vision lenses, and also of single-vision lenses withprismatic action, the spectacle lens 2 is modified in the surroundingsof the viewing point 8 by inserting an asphere.

Particularly in the case of spectacle lenses, the number of dioptricactions are used to distinguish between double-vision lenses (bifocallenses) and triple-vision lenses (trifocal lenses) . The two parts ofthe double-vision lens, that is to say the distance-vision part andreading area, have a different refractive power and are intended, inparticular, for presbyopes, who require both a lens for the far distanceand one for the near distance. If the reading area is further split intoa part for the reading distance and one for middle distance having, forexample, half the action of the full reading area, a triple-vision lensis spoken of, that is to say a lens having three actions.

In the case of bifocal lenses, which have a fused reading area, theseparation surface between the main lens and the material of the readingarea can be appropriately configured. In this case, an asphere isinserted once in the distance-vision part and once in the reading area.The transition of the region of maximum visual acuity 8 into the normalregion of the spectacle lens 2 of slightly reduced visual acuity can beperformed either abruptly at an edge or else by a soft or smoothtransition. Progressive lenses are used for such a smooth transition.

A progressive lens is understood as a spectacle lens 2 having anon-rotationally symmetrical surface with a continuous change in thefocusing action over a part of the entire area of the spectacle lens 2.In order to correct the spherical aberration in the case of progressivelenses, the surroundings of the two viewing points for the far distanceand the near distance are thereby respectively modified. It is alsopossible, if desired, for the progression zone to be incorporated.

FIG. 5 shows the spherical aberration of a normally seeing (emmetropic)eye 1 as a function of the pupil diameter p. It is to be seen that thespherical aberration is correlated with the magnitude of the pupildiameter p. This means that the spherical aberration also grows as thepupil 5 becomes larger. In this exemplary embodiment, the pupil diameterp has a magnitude of 6 mm. For beams 3 in the vicinity of the edge ofthe pupil, the eye 1 is myopic with an ametropia of −0.5 dpt. For apupil diameter p of 2 mm, the spherical aberration is approximately−0.075 dpt. The aberration of higher order or the spherical aberrationis assumed in the exemplary embodiment to be rotationally symmetricalover the pupil 5, and can therefore be represented by its cross section.

FIG. 6 illustrates the sagitta h of the correction of the sphericalaberration as a function of the pupil diameter p for a spectacle lens 2of 0 dpt bending and the refractive index n=1.6. For the spacing betweenthe vertex S of a curved refracting surface and the nadir point L of theperpendicular to the optical axis, the sagitta h is denoted by the pointof incidence A of a beam striking at the height H (FIG. 7). Thisexemplary embodiment illustrates which correction must be applied to theeye-side surface 9 of the spectacle lens 2, which is illustrated in FIG.4, in order to correct the spherical aberration described in FIG. 5. Itis easy to see that what is involved in this case is a surface deviatingfrom the spherical shape, that is to say an aspheric surface.

The lens 2 has refractive and/or diffractive structures in at least onerefracting surface that serves the purpose of dioptric correction of anametropia, and of the correction of at least one aberration of higherorder for at least one direction of view. It is preferred to provideonly one surface 9 or 10 of the lens 2, in particular of the spectaclelens, with such structures. This surface 9 or 10 preferably has onlyrefractive structures. Diffractive structures can be used, for example,for contact lenses and spectacle lenses. Thus, very many concentricallyarranged rings in microscopically fine steps can be provided on the rearof a contact lens. These “grooves” cannot be seen or perceived with thenaked eye. However, they fill up with tear liquid. Together, these twostructures produce a division of the light in addition to a refractionof the light. A lens 2 is thus created which has a multiple-visionaction with a transferring depth of focus. Visual impressions from nearto far can be imaged on the retina 7 simultaneously and with differingsharpness.

The spherical aberration, but also any other aberration of higher order,can thereby be substantially reduced or removed by the use of asphericsurfaces. At least 50%, preferably 75%, of the errors of higher ordercan be compensated solely by correcting the central aberrations, such assphere, cylinder and axis. It would also be conceivable for theaberrations of higher order to be compensated by correction measuressuch as, for example, applying an appropriately calculated correctingsurface (asphere, atorus or free form surface) to at least onerefractive surface 9 and/or 10 of the lens 2, preferably of thespectacle lens. However, it was also possible to establish that acorrection of the spherical equivalent (sph+zyl/2), for example, isgenerally already sufficient for also compensating at least 50% of thespherical aberration.

At least 50%, preferably 85%, of the spherical aberration can becompensated solely by the correction of the central aberrations. Thenumber of the parameters needing to be taken into account when producinglenses, in particular spectacle lenses, can thereby be reduced to thecentral aberrations. Consequently, it is possible to replace relativelycomplex surfaces, for example free form surfaces, by simple structuredsurfaces, for example a rotationally symmetrical aspheric surface, andthis simplifies the production.

1. A method for producing a lens, in particular a spectacle lens,wherein central aberrations of an eye, to be corrected, of an ametropicperson, such as sphere, cylinder and axis, being compensated, wherein atleast one refracting surface of said lens is configured in a way thatfor at least one direction of view both a dioptric correction of theametropia is performed and aberrations of higher order whose effects onthe visual acuity and/or contrast viewing are a function of the size ofthe pupillary aperture of said eye to be corrected, are corrected bysaid lens.
 2. The method as claimed in claim 1, wherein a sphericalaberration is corrected as aberration of higher order.
 3. The method asclaimed in claim 1, wherein a coma is corrected as aberration of higherorder.
 4. The method as claimed in claim 1, wherein a trefoil aberrationis corrected as aberration of higher order.
 5. The method as claimed inclaim 1, wherein values required for correcting said aberrations aredetermined by measuring visual acuity, in particular by determiningrefraction and/or by measuring a wavefront and/or by measuring awavefront and/or by skiaskopy.
 6. The method as claimed in claim 5,wherein said wavefront is measured with a Hartmann-Shack sensor.
 7. Themethod as claimed in claim 1, wherein the size of said pupillaryaperture is determined for correcting said aberrations, in particularsaid aberrations of higher order.
 8. The method as claimed in claim 1,wherein at least 50%, preferably at least 75%, of said aberrations ofhigher order are compensated solely by a correction of said centralaberrations such as sphere, cylinder and axis.
 9. The method as claimedin claim 1, wherein at least 50%, preferably at least 85%, of saidspherical aberration, is compensated solely by a correction of saidcentral aberrations, such as sphere, cylinder and axis.
 10. The methodas claimed in claim 1, wherein a region of highest visual acuity isformed by introducing at least one aspheric surface.
 11. The method asclaimed in claim 1, wherein a region of highest visual acuity is formedby introducing at least one atoric surface.
 12. The method as claimed inclaim 1, wherein a region of highest visual acuity is formed byintroducing at least one free form surface.
 13. The method as claimed inclaim 1, wherein a region in said lens is corrected for an infiniteobject distance.
 14. The method as claimed in claim 1, wherein a regionin said lens is corrected for a finite object distance.
 15. The methodas claimed in claim 1, wherein a transition of a region with highestvisual acuity into a region with slightly reduced visual acuity isperformed via an edge.
 16. The method as claimed in claim 1, wherein atransition of a region with highest visual acuity into a region withslightly reduced visual acuity is performed smoothly.
 17. A lensproduced according to one the method of claim 1, characterized by adesign as a spectacle lens, contact lens or intraocular lens.
 18. Thelens as claimed in claim 17, characterized by refractive and/ordiffractive structures in at least one refracting surface, both for thedioptric correcing surface, both for the dioptric correction of anametropia and for the correction at least of one aberration of higherorder for at least one direction of view.
 19. The lens as claimed inclaim 17, characterized by materials of glass and/or plastic.